Such a conventional motor controller for suppressing mechanical resonance is disclosed, for example, in Unexamined Japanese Patent Publication No. 2003-52188.
In the following, the conventional motor controller is described with reference to FIG. 6. FIG. 6 is a block diagram showing a system configuration of the conventional motor controller.
This conventional motor controller 100 is connected to motor 101 and speed detector 103. Motor 101 is connected with load 102. Further, speed detector 103 measures a speed of motor 101, and outputs speed detection signal ωra of motor 101.
As shown in FIG. 6, motor controller 100 includes speed control section 104, first notch filter 105, high-pass filter 107, second notch filter 108, notch control section 109, and torque control section 106.
Speed control section 104 receives input of speed command signal ωri and speed detection signal ωra, and sends output of torque command signal τ1i. First notch filter 105 receives input of torque command signal τ1i from speed control section 104, and sends output of torque command signal τ2i. High-pass filter 107 receives input of speed detection signal ωra, and sends output of oscillation component signal x not smaller than a cutoff frequency. Second notch filter 108 receives input of oscillation component signal x, and sends output of filtering result signal e. Notch control section 109 successively modifies notch frequencies fn of second notch filter 108 and first notch filter 105 so as to reduce an amplitude of filtering result signal e. Torque control section 106 receives input of torque command signal τ2i from first notch filter 105, to control motor 101.
Here, notch frequency fn of first notch filter 105 is obtained and set in the following manner.
First, oscillation component signal x not smaller than the cutoff frequency is extracted from inputted speed detection signal ωra by high-pass filter 107, and then outputted into second notch filter 108. Second notch filter 108 receives input of this oscillation component signal x, and sends output of filtering result signal e. Notch control section 109 successively modifies notch frequency fn of second notch filter 108 so as to reduce filtering result signal e from second notch filter 108. The setting of first notch filter 105 is changed such that notch frequency fn of this second notch filter 108 is set as the notch frequency of first notch filter 105.
In the conventional motor controller as thus configured, even when oscillation occurs due to mechanical resonance for some reason, the oscillation is suppressed since notch frequency fn of first notch filter 105 is successively modified so as to reduce an oscillation component, thereby suppressing the oscillation. For this reason, a system using the conventional motor controller comes into a stably controlled state.
However, the conventional motor controller detects an oscillation component due to oscillation, and then changes a notch frequency. Therefore, in a case where a resonance frequency frequently changes due to a conditional change such as a positional change of the load, the oscillation and the notch frequency are modified every time a deviation occurs between the resonance frequency and the notch frequency, causing a problem of preventing smooth movement.
For example, in the case of an apparatus in which a load position is changed by means of a motor, the resonance frequency changes significantly between a state where the load is close to the motor and a state where the load is far from the motor. When the load is reciprocated in such an apparatus, the resonance frequency of the apparatus changes significantly. Therefore, every time the deviation occurs between the resonance frequency and the notch frequency, oscillation occurs, though for a short period of time, and a behavior of modifying the notch frequency is repeated.